Oil and gas are produced from subsurface hydrocarbon bearing reservoir formations. One or more wells may be drilled to connect these subsurface hydrocarbon bearing reservoir formations to the surface allowing oil and gas to be released at the surface. Numerous of these subsurface hydrocarbon bearing reservoir formations are naturally fractured. Fractures can provide a major contribution to the permeability of the reservoir formation rocks to fluids. Considerable time and money is spent in the oil and gas industry to acquire fracture data using for instance borehole images and cores and to build discrete fracture network (DFN) models that are consistent with the data. In order to use the DFN models for dynamic flow simulations, it is known in the art to translate the DFN model to a grid-based set of effective permeability properties. This is known in the art as “upscaling”.
SPE paper 154369 “Static and Dynamic Assessment of DFN Permeability Upscaling” by M. Ahmed Elfeel and S. Geiger describes two main upscaling methods used in the industry: Oda's method and a flow-based method. Oda's method uses an analytical expression of an effective permeability tensor by adding weighted fracture permeabilities regardless of whether the fractures within the grid cell percolate. Hence, Oda's method is known to over-estimate permeabilities, particularly in poorly connected fracture networks. Flow-based methods calculate permeability of each grid cell by computational flow simulations on each grid cell based on the fractures that are present in the grid cell. This is computationally extensive and the end result has been found to be sensitive to orientation and size of the grid cells compared to the DFN model.